1. Field of the Invention
The present invention relates to wire bonders and more particularly concerns detection of a missing wire in a transducer driven bonder.
2. Description of Related Art
In many types of ultrasonic wire bonders wire is fed to and under the bonding tool which presses the wire downwardly against a circuit element to perform an ultrasonic bond at that point. Wire is paid out from a wire supply that is mounted to move with the tool by moving the tool and supply relative to the prior bond to which the wire is still secured. Then a second bond is made at a second point or circuit element, after which a length of fresh wire is paid out, by again moving the tool, to prepare for the next pair of bonds. The wire then is clamped to the tool, and by moving the tool, with the wire clamped thereto, relative to the bonds, the wire is broken at the last bond. The wire and tool are then moved to the location for the next bond. At times the wire may be improperly fed, may break between first and second bonds, or for some other reason the apparatus may fail to properly feed wire to and under the tip of the bonding tool, thereby preventing making of any subsequent bonds until the wire feed problem has been detected and corrected. In an automatic machine, the loss of wire may be undetected, and the machine may continue through its programmed operations without doing any useful work.
In the so-called ball bonder, which requires a ball on the leading edge of a wire for the first bond, a wire end ball is created by feeding a current through the wire, which is temporarily connected to portions of a wire end ball forming circuit. A missing wire is readily detected in such an arrangement by noting absence of current in the ball forming step. However, in many bonders, this ball forming step is not employed, and in such bonders there have been no known methods or arrangements for detecting a missing wire. Therefore, if wire is not properly fed in an automatic bonding machine, the apparatus may continue to operate, as previously mentioned, moving through its various positions, but all without any useful effect because there is no wire at the tip of the bonding tool.
Accordingly, it is an object of the present invention to provide for detection of a missing wire in a transducer driven wire bonder.